1. Field of the Invention
The present invention relates to an optical element, a method for manufacturing the optical element and a semiconductor laser device using the optical element.
2. Description of the Related Art
In recent years, research on a photonic crystal has been actively conducted.
The photonic crystal means a structure which is formed of substances periodically repeating different refractive indices, and thereby causes a wavelength range (photonic band gap) in which light is inhibited from propagating, similarly to a band gap existing in an electronic state of a crystal.
By using the photonic crystal, it becomes possible to two-dimensionally or three-dimensionally confine light in the crystal, so that the photonic crystal is tried to be applied to an optical waveguide or a mirror for a semiconductor laser.
Technologies with the use of various techniques have been proposed in order to produce the two-dimensional and three-dimensional dielectrics with the periodic structure for the photonic crystal. However, the photonic crystal having the two-dimensional periodic structure is more likely to be realized because the structure can be produced with a lithographic technology.
Incidentally, an ideal two-dimensional photonic crystal shall have a uniform and infinite length in a Z-axis direction, but it is practically impossible to produce such a crystal. In addition, when the two-dimensional photonic crystal is long in the Z-axis direction (film thickness direction), light inevitably spreads toward outside of the Z-axis direction. Accordingly, when the two-dimensional photonic crystal is imparted a function such as amplification and absorption, the length brings disadvantage.
For this reason, when the two-dimensional photonic crystal is actually used, it needs to confine the light which propagates in the Z-axis direction, by any means.
Specifically, it is necessary to make a difference between refractive indices of a photonic crystal layer placed on a substrate and the substrate large.
In order to meet such a need, for instance, Japanese Patent Application Laid-Open No. 2000-232258 (Patent Document 1) discloses a technology in FIG. 2 for realizing a slab-type photonic crystal formed of two layers having a large difference of a refractive index between them by combining a semiconductor layer with a dielectric layer while using a stacking technique.